Vapor-liquid contact apparatus



Nov. 29, 1955 P. LAMBERT 2,725,343

VAPOR-LIQUID CONTACT APPARATUS Filed June 19, 1951 Top or Tan EA I INVENTOR flerreZawe/l 2' 2 VAPOR-LIQUID CONTACT APPARATUS Pierre Lambert, Chappaqua, N. Y., assignor to The Lummus Company, New York, N. Y., a corporation of Delaware Application June 19, 1951, Serial No. 232,279

3 Claims. (Cl. 196-114) This invention relates to improvements in vapor-liquid contact apparatus and, more particularly, to an improved deck construction for distillation and similar towers or columns.

In the field of distillation, it is recognized that there are critical dimensions which control the ultimate diameter and height of tower. Usually a sharp jump in cost of such equipment takes place between the so-called shopfabricated tower and the alternate field-fabricated tower. When the former exceeds about fourteen feet in diameter, it is not usually possible to ship it by rail, and when a tower is sixteen to twenty feet in diameter, its cost is no longer proportional to its size.

My present invention is particularly applicable to distillation towers or columns which have a very high throughput but in which relatively few decks are required. By my arrangement of certain of the decks as offset in part from the plane of the balance, I can obtain the necessary fractionation, within the limit of vapor velocities and still obtain a reduction in diameter of the tower in the order of fifteen to twenty-five percent, and with no material increase in height.

It is my principal object of the invention to provide a unique deck arrangement that will reduce the cost of tower construction.

Further objects and advantages of my invention will appear from the following disclosure of a preferred form of embodiment thereof, taken in conjunction with the drawing attached in which:

Fig. 1 is a partial central vertical section of a fractionating column, having offset bubble decks in accordance with my invention.

Fig. 2 is a graphical analysis of the vapor loading at various points in towers having different types of decks showing the limiting factors of size. I

In accordance with my invention, I have shown, in Fig. 1, a distillation tower 10, such as would be used for a vacuum distillation of a topped crudev oil. The hot, partially vaporized oil is passed from a heater, not shown, through the transfer line 11 to flash zone 13 of the tower Iii. Steam may be introduced to line 11 through line 12, or elsewhere if desired. The lighter ends of the hot oil are vaporized, the vapors rising upwardly through the tower to be separated into, perhaps, a light and heavy gas oil, and an intermediate paraflin distillate, depending on the nature of the charge stock in line 11. Heavier, nonvaporized materials are passed from flash zone 13 to a lower stripping section 14 which contains a plurality of contact decks 15. Stripping steam may be introduced through line 16 to completely volatilize the lighter constituents from the vacuum bottoms. Thus, a comparatively heavy asphalt may be withdrawn from the lower portion of the stripping section 14. This section is generally of smaller diameter than the rest of the t'ower because the vapor loading is substantially nil, it being only necessary to provide for the volume of steam plus a small proportionof liberated vapors.

The vapors flashed ofl in the flash" zone 13 pas sup- States Patent wardly through the lower rectifying section 17, hereinafter described in detail, and thence upwardly through upper rectifying section" 18 from which various side streams may be withdrawn.

It is generally well-known that in a distillation system wherein a separation such as that above described is made in a tower such as tower iii, that the vapor load and the liquid load increase up the tower. Under these conditions, it is found desirable to employ shower decks in the upper part of the tower, mainly because, due to the character of these shower decks in permitting high vapor velocities, the diameter of the tower is proportionately decreased.

in the lower portions of a distillation tower, the liquid load decreases more rapidly than the vapor load to a point at which shower decks no longer maintain their highly eflicient performance. Thus it is desirable or necessary to use bubble decks in the lower portion of the rectifying zone immediately above the flash zone. A bubble deck can maintain its high efiiciency at much lower liquid loads than can a shower deck. However, under these conditions, the bubble deck must be of greater diameter in order to provide for sufiiciently low vapor velocities. Thus the minimum diameter for a tower may be set under this condition by the requirements of the few decks above the flash zone, since the upper section containing shower trays may be smaller.

This condition is qualitatively shown in Fig. 2 which graphically represents the vapor load in various portions of the tower. The ordinate represents the various positions in the tower extending upwardly from the flash zone, at the bottom of the axis, to the top of the tower at the upper end of the axis, and when taken in coordination with each of the three parametric equations, A, B, and C, represents the required vapor area, and thus the diameter of the tower, for each of the different types of decks.

Curve A shows the required vapor area for shower decks and curve C shows the area required for bubble decks. Because of the conditions hereinbefore set forth, as we progress downwardly from the top of the tower, the required vapor area follows curve A from point E to F. Reaching the lower rectification section where bubble decks are substituted for shower decks, the requiredvapor area curve follows path P, G, H, I. The

1 point H thus marks the minimum diameter of the tower.

(It is noted that by-and-large it is more economical to maintain a common diameter throughout most of the tower height than to change according to the vapor requirements of each section.)

In order to minimize the required vapor area of a tower and to eliminate the problems hereinbefore set forth, .i have developed a new, improved type of tray construction. in tower 10, shower trays 19, 2d, 21, 22, and 23 form part of the upper rectification section. These trays are of standard form, and contain weirs to maintain a liquid level thereon as well as holes whereby liquid may drip down to the next lower deck. A liquid draw-oft line 24 may be provided for removing a side stream product such as a heavy gas oil, a portion of which may be returned as ci culating reflux through line 25.

Lower shower deck 23 may contain a drawoff pot 25 from which line 24% leads, and also two conduits 27 and 28 leading to my improved special off-set decks. As disclosed in this embodiment, the lower rectifying section 17 includes two pairs 29 and 35B of off-set decks. The lower pair 29 includes a single deck 31 extending from the shell 19 of the tower a substantial distance thereacross. The inner edge 32 may be straight thus making the deck in the form of a segment of a circle having an arc greater than 180."; i. e., the deck will extend past the center of the tower and may cover as much as of the area of the tower. A downcomer 35 leads from a draw-off compartment on deck 31 to deck 36 which may be of shape substantially identical to deck 31 and which may contain the same type of contact devices; i. e., bubble caps or the like. Liquid may be removed from deck 3-6 by downcomer 37 from which it is passed to the stripping zone of the tower.

The upper section 39 of off-set decks is similarly constructed. Upper deck 58 extends from a point on the shell of tower diametrically opposite from and above the point from which deck 31 extends. The inner edge will overlap the inner edge of deck 31; i. e., deck 38 will also be a segment of a circle of arc greater than 180. Downcomer 39 leads to deck iii which is generally similar to deck 38. Downcomer 4]. leads from deck 40 also to the lower stripping zone of the tower.

Where the downcomers 35 and 37 are pipes, the decks 31 and 36 are substantially identical in shape. The downcomer may also, of course, be fabricated as shown in section 30; i. e., a straight piece of metal leading from the upper deck to the lower deck and the lower deck to the stripping zone. When the downcomer is thus fabricated, it may be proper to describe the lower deck of a pair as zone-shaped; i. e., bounded by two parallel straight sides and two intercepted arcs of the same circles.

The inner edges of the decks in section 29 are joined by the wall 33 and the inner edges of the decks in section 3d are joined by well 42. The lower edge of wall 42 is joined to the upper edge of wall. 33 by wall 43. Thus the deck sections are completely separated from the vapor passageways 34 and 44.

By means of these improved construction decks, it is possible to provide about 1.6 times as much vapor area per sq. foot of tower cross-section area; i. e., it is posible to make a tower having about 62.5% less area to perform a given separation than would be possible with bubble decks. In one case the improvement permitted a reduction in tower diameter from 23 feet to 18 feet, six inches.

Referring to Fig. 2' once again, the vapor-loading curve for the new, improved ofl-set decks is shown as curve B. It is noted that they require less vapor area than bubble decks. As we traverse the tower from top to flash zone,- the required vapor area curve follows the path E, F, G, K. Thus, point G determines the actual tower diameter, rather than. point H, as is the case with bubble decks.

In operation half the'vapors ascending from the flash zone will pass upwardly through vapor passage 34 and the other half passes through section 29. The portion ascending passage 34 passes through section 30. The other portion, after passing through section 29, passes through passage 44, after which it joins with the vapors from section 30.

The downflowing liquid is divided into two streams by downcomers 27 and 28. Each stream passes through a separate section, and the eflluent is joined in the stripping action.

FIOHI the foregoing description, it is believed that the invention may be readily understood by those skilled in the art, and it is manifest that changes may be made in the details set forth without departing from the spirit of the invention, as expressed in the following claims.

What is claimed and desired to be secured by Letters Patent is:

1. A vacuum distillation column which comprises a flash zone, means to introduce a multi-component hydrocarbon feed thereto, a low vapor velocity rectifying zone above said flash zone including independent, vapor-liquid contact sections positioned on alternate sides of the tower one substantially above the other, each of said vaporliquid contact sections having at least one segment shaped bubble deck extending from the column wall across the greater portion of the cross-sectional area of the column, said bubble deck having a plurality of bubble caps and risers thereon, a vapor-tight partitionabutting the inside edges of the bubble decks in each contact section, said partition extending from the bottom bubble deck in the lower section to above the top deck in the upper section so as to define independent vapor passageways within the tower, an upper high vapor velocity rectifying zone above said low velocity rectifying zone, said upper rectifying zone having a plurality of shower decks therein, separate downcomers extending from the lowermost shower deck of said upperrectifying zone to each of the separate vapor-liquid contact sections of the lower rectifying zone, and means within said separate vapor-liquid sections to provide a liquid seal for the lower end of said downcomers.

2. A vacuum distillation column for the distillation of a topped crude to produce an intermediate gas oil, a stripped bottoms and a light distillate overhead which comprises, a lower flash zone, means to introduce a topped crude thereto, a lower rectifying zone above said flash zone, said lower rectifying zone including independent vapor-liquid. contact sections positioned on alternate sides of the tower one above the other, each section having at least one segment-shaped bubble deck extending from the column wall across the greater portion of the cross-sectional area of the column, said bubble decks having a plurality of bubble caps and risers thereon, a vapor tight partition abutting the inside edges of the bubble deck in each contact section, said partition vertically extending from the bottom deck in the lower section. to above the top deck in the upper section thereby defining independent vapor-tight passageways in the respective contact sections, an upper rectifying zone above said lower rectifying zone, said upper rectifying. zone having a plurality of shower decks therein, means to feed a liquid reflux to said shower decks, means'to withdraw a gas oil sidecut at approximately the bottom of said upperrectifying zone, separate downcomers extending from the lowermost shower deck of said upper rectifying zone to each of the separate vaporliquid contact sections of the lower rectifying zone, means on said top segment-shaped bubble decks to maintain a liquid level above the lower ends of said downcomer, a bottomstripping zone below said flash zone and means to introduce a stripping medium to the lower portion of said stripping zone.

3. A vacuum distillation column for the distillation of a topped. hydrocarbon crude to produce an intermediate gas-oil, a stripped bottoms and a light gas-oil overhead which comprises, a flash zone in the lower part of. said column,.means to introduce a topped crude thereto, a rectifying zone above said flash zone consisting of lower. and. upper sections, said lower rectifying section including at. least two vapor-liquid contact sections, said sections positioned on alternate sides of the tower: one above the. other, each of said sections having at least one segment-shaped bubble deck extending from the column wall across the greater portion of the crosssectional. area of the column, said bubble decks having a plurality of bubble caps and risers thereon, a vapor tight partition abutting the: inside edges of the bubble deck in each of said. contact sections, said partition extending from the bottom deck in the lower section to above the top deck in the upper section thereby defining independent vapor-tight' passageways in the respective contact sections, an upper rectifying section above said lower rectifying section, said upper rectifying sectionhaving a plurality of shower decks therein, means to feed a liquid. reflux to said shower decks, means to withdraw a gas-oil side cut. from the lower portion of said upper-rectifying section, separate liquid downcomers extending-from the lowermost shower deck of said upper rectifying section to the top segment-shaped bubble deck in each of the separate vapor-liquid contact sections of the lower rectifying sections, means on said top segment-shaped bubble deck in each section. to maintain a liquid. level abovethe lower ends of saiddowncomer,

separate liquid downcomers extending from the lowermost bubble deck in each of said vapor-liquid contact sections to the bottom of said flash zone, a bottoms stripping zone below said flash zone and means to introduce a stripping medium to the lower portion of said stripping zone.

References Cited in the file of this patent UNITED STATES PATENTS 368,208 Harris Aug. 16, 1887 6 Bradburn Oct. 22, 1895 Carrier May 4, 1915 Lewis Aug. 14, 1928 MacKinzie Nov. 25, 1930 Ragatz May 10, 1938 Schulze et a1. Oct. 8, 1940 Kraft May 29, 1945 Dice Oct. 9, 1951 

1. A VACUUM DISTILLATION COLUMN WHICH COMPRISES A FLASH ZONE, MEANS TO INTRODUCE A MULTI-COMPONENT HYDROCARBON FEED THERETO, A LOW VAPOR VELOCITY RECTIFYING ZONE ABOVE SAID FLASH ZONE INCLUDING INDEPENDENT, VAPOR-LIQUID CONTACT SECTIONS POSITIONED ON ALTERNATE SIDES OF THE TOWER ONE SUBSTANTIALLY ABOVE THE OTHER, EACH OF SAID VAPORLIQUID CONTACT SECTIONS HAVING AT LEAST ONE SEGMENT SHAPED BUBBLE DECK EXTENDING FROM THE COLUMN WALL ACROSS THE GREATER PORTION OF THE CROSS-SECTIONAL AREA OF THE COLUMN, SAID BUBBLE DECK HAVING A PLURALITY OF BUBBLE CAPS AND RISERS THEREON A VAPOR-TIGHT PARTITION ABUTTING THE INSIDE EDGES OF THE BUBBLE DECKS IN EACH CONTACT SECTION, SAID PARTITION EXTENDING FROM THE BOTTOM BUBBLE DECK IN THEE PARTITION EXTENDING FROM THE BOTTOM BUBBLE DECK IN THE SO AS TO DEFINE INDEPENDENT VAPOR PASSAGEWAYS WITHIN THE TOWERM AN UPPER HIGH VAPOR VELOCITY RECTIFYING ZONE ABOVE SAID LOW VELOCITY RECTIFYING ZONE, SAID UPPER RECTIFYING ZONE HAVING A PLURALITY OF SHOWER DECKS THEREIN, SEPARATE DOWNCOMERS EXTENDING FROM THE LOWERMOST SHOWER DECK OF SAID UPPER RECTIFYING ZONE TO EACH OF THE SEPARATE VAPOR-LIQUID CONTACT SECTIONS OF THE LOWER RECTIFYING ZONE, AND MEANS WITHIN SAID SEPARATE VAPOR-LIQUID SECTIONS TO PROVIDE A LIQUID SEAL FOR THE LOWER END OF SAID DOWNCOMERS. 